Apoptotic cells are rapidly cleared by phagocytosis in vivo. Defects in apoptotic cell phagocytosis have been implicated in several human pathologies such as Systemic Lupus Erythematosus. In the absence of engulfment, the remaining tissue may be damaged by exposure to the contents of the dying cells. In Drosophila, apoptotic corpses are rapidly engulfed by circulating phagocytic cells. We have shown that the croquemort gene is required for the efficient engulfment of apoptotic cells in the embryo. We propose to identify and characterize other genes involved in engulfment, using a combination of Drosophila genetics, tissue culture assays and differential expression screens. A screen of genomic deletions identified a number of regions required for efficient engulfment of apoptotic cells in the embryo. One of the genomic regions identified in our screen contains the Drosophila homologue of the phosphatidylserine receptor. This receptor has been implicated in the phagocytosis of apoptotic corpses in mammalian tissue culture assays. Although we do not detect a major role for this receptor in engulfment in the Drosophila embryo, we do find that it functions to inhibit apoptosis. We will use this phenotype to screen for signaling pathways activated by the receptor. In addition, we will further explore the requirement for this receptor in engulfment. These studies will provide insight into the general function of the protein. We have also identified other genomic regions that contain genes required for engulfment. We will distinguish the responsible genes using genetic and RNA interference techniques. A tissue culture based apoptotic cell engulfment assay has been developed to facilitate RNAi techniques. This will allow us to examine the role of genes required in both the phagocyte and in the apoptotic target cell. In our initial studies, we found that croquemort levels were upregulated in the presence of apoptotic cells. To identify other genes in the phagocyte that show changes in expression on exposure to apoptotic cells, we have initiated a differential expression screen. Genes that show expression changes in response to the presence of apoptotic cells will be tested for a role in engulfment in tissue culture and in vivo. This combination of strategies will allow us to identify and characterize many genes involved in apoptotic cell engulfment, and to understand how they function in this important process. [unreadable] [unreadable] [unreadable] [unreadable]